In recent years, flat panel display devices that use flat panel display elements such as liquid crystal panels and plasma display panels are increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tube displays, allowing image display devices to be made thinner. Liquid crystal panels used in liquid crystal display devices do not emit light on their own, and therefore, it is necessary to provide a separate backlight device as an illumination device. A known example of such a backlight device is an edge-lit type backlight device in which a light-receiving face is provided on a side face of a light guide plate, and a light source such as an LED is provided facing the side face of the light guide plate.
In the edge-lit type backlight device, a light guide plate is housed in a chassis, which is provided as a case. In some cases, a reflective sheet that reflects light leaked from the light guide plate back to the light guide plate is disposed on a surface of the light guide plate that faces a bottom of the chassis. By having such a reflective sheet, the light leaking from the light guide plate and reflected by the reflective sheet is directed toward the display surface, and as a result, uneven brightness and the like on the display surface of the backlight device can be improved. Patent Document 1 discloses such a backlight device, for example.